Stress urinary incontinence (SUI) is the unintentional urine leakage during times of abdominal stress, such as occurs during coughing, laughing, or sneezing. One cause of SUI is inadequate anatomical support of the urethra which allows the urethra to move out of the retropubic space and rotate into the vagina. This condition is known as “hypermobility of the urethra” or simply “hypermobility”. SUI may also result from insufficient closing pressure of the urethra which prevents the urethra from fully collapsing and sealing. SUI can develop in men as a result of prostate surgery during which the voluntary sphincter mechanism is damaged either partially or totally.
Another medical condition suffered by women is pelvic organ prolapse (POP) which refers to prolapse of the organs (urinary bladder, intestines and uterus) normally positioned within the pelvis. Normally these organs are supported by the “pelvic floor”. Weakening of the pelvic floor allows herniation of these organs towards the vagina.
Another medical condition is fecal incontinence which is the inability to control bowel movements, causing feces to leak unexpectedly from the rectum. It may be due to a weakened anal sphincter associated with aging or to damaged nerves and muscles of the rectum and anus that can occur during childbirth.
Urethral slings have been used to treat hypermobility in women and postoperative incontinence in men. A urethral sling is typically implanted below the urethra to provide support under the urethra and prevent unwanted movement of the urethra towards the vagina or compress the male bulbous urethra. A variety of different slings have been developed that are implanted below the urethra to support it. In women, these slings are generally not intended to raise the urethra but to provide support for the urethra to prevent the unwanted downward urethral movement associated with hypermobility. A typical urethral sling comprises a strip of mesh that is implanted using a transvaginal approach in which opposite ends of the mesh are arranged on opposite sides (towards the sides or upwards) of the urethra so that the mesh loops under the urethra to form a sling. The mesh is typically implanted using needles that attach to the mesh of the sling so that the mesh ends can be inserted into the body and exit out of the body at a desired exit site and then are either anchored to the pubic bones or tissues, left under the skin, or in the periurethral or perivaginal space for self anchoring by tissue proliferation. Excess mesh extending out of the body can be removed and the remainder of the mesh left under the skin. During the first days after its implantation the unanchored sling is held in place by friction, then by tissue ingrowth through the interstices of the mesh.
POP can be repaired either by applying sutures to the pelvic floor to reshape the vagina and return the prolapsed organ to their normal position or by placing a layer of mesh to support the prolapsed organs. Surgery either through the vagina or through the abdomen (either open or laparoscopic) is the usual method of POP repair.
Fecal incontinence is treated by sphincteroplasty. Patients who are not suitable for such surgery or who have failed sphincteroplasty can be implanted a puborectal sling.
Mesh slings are generally successful in treating incontinence or POP but occasionally fail. One cause of failure is improper positioning of the sling, insufficient or excessive tension of the sling during implantation and dislocation of the sling sometime after implantation. Some of the complications which may develop after mesh implantation include failure of the sling to prevent incontinence, postoperative urine retention, sling caused bladder hyperactivity, coital pain, sexual impairment and/or discomfort, infection, vaginal and urethral tissue erosion. In some of these complications there may be an indication to remove the mesh sling. After tissue ingrowth into the spaces of the mesh, complete removal of the implanted mesh is very difficult. During the surgery or immediately after or within the first days after a mesh sling implantation, adjustment of a misplaced mesh sling can only be performed by pulling on the ends of the sling to increase the sling tension or releasing the tension through a vaginal incision. The extent of tension readjustement is limited even after a couple of weeks due to the tissue ingrowth and may not allow proper positioning of the mesh. Mesh slings do not allow late removal by simple surgery.
Some of the currently available mesh slings allow readjustment only after a few days following their implantation. United States Patent Publication 20080269547 to Hortenstine discloses an adjustable urethral mesh sling having an expansion chamber that is positioned under the urethra after implantation. A conduit in fluid communication with the expansion chamber allows remote expansion of the expansion chamber. The expanded chamber presses on the urethra and contributes to the closure of the urethral lumen during stress.
Any foreign body placed in a living tissue can elicit an inflammatory reaction in the surrounding tissue. This process is usually followed by gradual development of a cocoon-like collagen shell and/or fibrous tissue as a natural barrier around the foreign body (encapsulation). Mature cross-linked collagen and other extracellular matrix proteins gradually contribute to the formation of a hypocellular dense fibrous capsule that becomes impermeable or hypopermeable to many compounds. All soft-tissue implanted devices cause such a reaction. Since non-absorbable and biocompatible, smooth surfaced implants are unaffected by the biological activities of the surrounding tissues during the encapsulation process, they do not adhere to tissues and can be pulled-out easily at anytime. i.e. smooth surfaced monofilament surgical sutures remain within a smooth surfaced capsule and they can be pulled out at anytime much easily than a comparable multifilament braided sutures that are invaded by tissue. Other factors influencing the host response include implant location, size, shape, micromotion, surface chemistry, surface roughness, and porosity. (Dee K C, Puleo D A, Bizios R. Wound healing. In: An introduction to tissue-biomaterial interactions. Hoboken, N.J.: John Wiley & Sons Inc.; 2002). The process of capsule formation, as well as the structure of the final capsule, is similar in animal models and in humans. (Parker J A, Walboomers X F, Von den Hoff J W, Maltha J C, Jansen J A Soft-tissue response to silicone and poly-L-lactic acid implants with a periodic or random surface micropattern. J Biomed Mater Res. 2002; 61:91-98).